1. Field of the Invention
The present invention relates to a pilot signal reception method and receiver.
2. Description of the Related Art
In a CDMA communication, a pilot signal is used to acquire synchronization in a mobile station, create a delay profile and correct frequencies in a mobile station, and adjust reception timings in a mobile station, etc. This pilot signal is sent from a base station.
An IS-95-compliant communication system is provided with a dedicated pilot channel 100 as shown in FIG. 12A.
Furthermore, in a new standard W-CDMA system, a dedicated pilot channel 101 is provided in addition to a channel with pilot signals (PL) inserted at predetermined intervals.
That a dedicated pilot signal channel exists means that pilot signals are output from the transmitting side all the time.
A concrete pilot channel (100 and 101) format example is shown in FIG. 12C.
What is shown in the upper part of FIG. 12C is an example of a pilot signal subjected to data modulation (format example 1).
That is, in the case of format example 1, the pilot channel is configured by slots made up of a set of several to a few tens of symbols, which are information units spread using a specified number of spreading code chips.
Furthermore, in the example shown in the lower part of FIG. 12C (format example 2), no data modulation is applied to the pilot channel. For example, since a common pilot channel is commonly used by base stations, the common pilot channel need not be subjected to data (symbol) modulation and such a format without data (symbol) modulation (that is, format with no symbol concept) is also accepted.
Here, reception of a spread/modulated pilot channel will be considered.
When receiving pilot signals, it is desirable to intermittently receive the pilot signals rather than receiving the pilot signals all the time and thereby reduce the amount of pilot data in order to alleviate load on a circuit carrying out signal processing such as a DSP and reduce the amount of pilot data.
The inventor of the present invention has studied a method of performing despreading processing and then demodulation on a predetermined number of known symbols in slots at predetermined timings as shown in FIG. 14.
As a result, it has been discovered that reception according to this method provides cyclic and burst-like demodulation of pilot symbols, and therefore can provide reception with low reliability at most when the intensity of the signal is reduced due to cyclic fading or burst-like fading.
That is, as shown in the lower part of FIG. 14, in the case where a reception timing (reception segment) of a pilot signal coincides with a valley of cyclic variation of the intensity of the reception signal, an S/N (reception quality) with respect to reception of the pilot signal deteriorates. Therefore, the reliability of data in the reception segment is also reduced.
The present invention has been implemented focusing on such investigation results and it is an object of the present invention to attain reception of pilot signals with high reliability by reducing adverse influences of fading.